Exhaust gas recirculation (EGR) is used in internal combustion engine control. EGR circuits remove a portion of exhaust gas flow from the exhaust system for ingestion as part of the cylinder charge. EGR circuits are known for use in many different engine types and configurations, for instance in both diesel and gasoline engines.
Combustion is highly dependent upon the conditions existing within the combustion chamber. Variations in properties such as temperature within the combustion chamber can cause adverse effects upon the resulting combustion. The temperature of the EGR flow channeled into the combustion chamber has effects upon the overall temperature within the combustion chamber. As a result of the need to control these temperatures, methods are known to modulate the temperature of EGR flow within the EGR circuit through the use of an EGR cooler including a heat exchange device.
Heat exchange devices can take many forms. One known heat exchange device is a gas to liquid type heat exchanger. Another known heat exchange device is a gas to gas type heat exchanger. Efficient heat transfer generally requires large surface areas through large cross sectional flow paths. Flow velocity generally decreases as cross sectional flow path increase.
EGR flows contain by-products of combustion. Particulate matter (PM) and other combustion by-products travel through the exhaust system with the exhaust gas flow. The EGR circuit, by tapping into the exhaust system, is exposed to these by-products. Heat exchangers can include narrow and subdivided passages in order to maximize heat transfer from the hot gas to the cooling liquid. However, narrow passages with large surface areas can act as filters to the combustion by-products, collecting particulate deposits on the surfaces within the passages. Additionally, testing has shown that lower exhaust gas velocities, such as tend to exist within a heat exchanger, increasing the rate at which particulate deposits are left on the surfaces. Such deposits within the heat exchanger can have a number of adverse effects upon the heat exchanger, including but not limited to corrosion, increased flow resistance, flow blockage, reduction of heat transfer capacity, and noise, vibration and harshness (NVH).